The purpose of this project is to study the synthesis of alpha-lactalbumin and casein protein and their mRNAs in the mammary tumors during growth and regression. The results have shown that MTW9 mammary tumors whose growth is dependent on mammotropic stimulus, synthesize alpha-LA and caseins. Withdrawal of mammotropic hormones arrests the synthesis of alpha-LA and 42K casein proteins as early as six hours after the onset of regression. Alpha-LA mRNA levels compared with the growing tumors were reduced at this time of regression.